Over the past 250 years, the number of "planets" in our solar system has ranged from six to nine — and, briefly, even 11 — depending on what astronomers knew at the time and how they defined a planet.

Planets without stars to orbit raise important questions about how planets evolve and what habitability might look like across the cosmos.

Astronomers are investigating a strange class of exoplanets known as eccentric warm Jupiters — massive gas giants that orbit their stars in unexpected, elongated paths. Unlike their close-orbiting ...

Astronomers are closing in on one of the most tantalizing possibilities in planetary science, evidence that a previously unknown world may be lurking in the outer reaches of the solar system. The ...

An exoplanetary system about 116 light-years from Earth could flip the script on how planets form, according to researchers who discovered it using telescopes from NASA and the European Space Agency, ...

Seoul National University astronomer traces crystalline silicate transport to comets and planetary building blocks over 4.6 ...

James is a published author with multiple pop-history and science books to his name. He specializes in history, space, strange science, and anything out of the ordinary.View full profile James is a ...

Dying stars may be wiping out nearby giant planets as they expand into red giants. Astronomers found that these close-in planets become increasingly rare around more evolved stars, suggesting many ...

Learn how Pluto nearly kept its planet status in a proposed 12-planet Solar System as its demotion marks its 20th anniversary. Eight days before Pluto lost its planetary status, it appeared ready to ...

Even at a glance, the planets in our solar system are wildly diverse. Huge and small, airless and densely packed with atmosphere, they have a wide range of characteristics distinguishing them. But if ...

Our definition of a planet has changed over the years — causing a bit of confusion. | Credit: wasan prunglampoo/Getty Images Over the past 250 years, the number of "planets" in our solar system has ...